This invention relates to measuring the time intervals of one or more events with respect to a reference time or event.
It is often necessary to measure the time lapsed from a reference time or event to one or more following events using digital counting techniques. When a relatively slow clock rate may be utilized to measure time, i.e., when the clock period is long relative to the propagation time of the counter, the counter is easily read out and stored upon the occurrence of an event in an interval between clock pulses. To assure that the counter is read out while in a stable state, the read-out pulse generated by the event being timed is synchronized with the clock pulses.
As the period of the clock approaches the propagation time of the counter, a problem arises in having sufficient time to read out the counter after allowing for the maximum propagation time of carries through the counter. In other words, if the propagation time of the counter is too long relative to the period of the clock pulses, there may be very little or no stable period for reading out the counter between successive clock pulses. The problem then is to provide a way of reading out the counter without interrupting the operation of the counter.